This is a first pass at implementing
[P2841R7](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2025/p2841r7.pdf).
The implementation is far from complete; however, I'm aiming to do that
in chunks, to make our lives easier.
In particular, this does not implement
- Subsumption
- Mangling
- Satisfaction checking is minimal as we should focus on #141776 first
(note that I'm currently very stuck)
FTM, release notes, status page, etc, will be updated once the feature
is more mature. Given the state of the feature, it is not yet allowed in
older language modes.
Of note:
- Mismatches between template template arguments and template template
parameters are a bit wonky. This is addressed by #130603
- We use `UnresolvedLookupExpr` to model template-id. While this is
pre-existing, I have been wondering if we want to introduce a different
OverloadExpr subclass for that. I did not make the change in this patch.
The mangling compatibility being tested here changed between Clang 17
and 18, not between 16 and 17, so change the "old" version to 17.
As requested by @ahatanak in [post-commit
review](7421dd55a1 (commitcomment-128651446)).
This patch will finally allow us to mark C++17 support in clang as
complete.
In order to implement this as a DR and avoid breaking reasonable code
that worked before P0522, this patch implements a provisional resolution
for CWG2398: When deducing template template parameters against each other,
and the argument side names a template specialization, instead of just
deducing A, we deduce a synthesized template template parameter based
on A, but with it's parameters using the template specialization's arguments
as defaults.
The driver flag is deprecated with a warning.
Fixes https://github.com/llvm/llvm-project/issues/36505
before mangling the template argument list.
With an abbreviated function template, the template parameters can
contain constraints that refer to the function parameters, so we need to
bring the function parameters into scope earlier.
Fixes#67356.
This implements proposals from:
- https://github.com/itanium-cxx-abi/cxx-abi/issues/24: mangling for
constraints, requires-clauses, requires-expressions.
- https://github.com/itanium-cxx-abi/cxx-abi/issues/31: requires-clauses and
template parameters in a lambda expression are mangled into the <lambda-sig>.
- https://github.com/itanium-cxx-abi/cxx-abi/issues/47 (STEP 3): mangling for
template argument is prefixed by mangling of template parameter declaration
if it's not "obvious", for example because the template parameter is
constrained (we already implemented STEP 1 and STEP 2).
This changes the manglings for a few cases:
- Functions and function templates with constraints.
- Function templates with template parameters with deduced types:
`typename<auto N> void f();`
- Function templates with template template parameters where the argument has a
different template-head:
`template<template<typename...T>> void f(); f<std::vector>();`
In each case where a mangling changed, the change fixes a mangling collision.
Note that only function templates are affected, not class templates or variable
templates, and only new constructs (template parameters with deduced types,
constrained templates) and esoteric constructs (templates with template
template parameters with non-matching template template arguments, most of
which Clang still does not accept by default due to
`-frelaxed-template-template-args` not being enabled by default), so the risk
to ABI stability from this change is relatively low. Nonetheless,
`-fclang-abi-compat=17` can be used to restore the old manglings for cases
which we could successfully but incorrectly mangle before.
Fixes#48216, #49884, #61273
Reviewed By: erichkeane, #libc_abi
Differential Revision: https://reviews.llvm.org/D147655
Previously, we were emitting an extraneous X .. E in <template-arg>
around an <expr-primary> if the template argument was constructed from
an expression (rather than an already-evaluated literal value). In
such a case, we would then e.g. emit 'XLi0EE' instead of 'Li0E'.
We had one special-case for DeclRefExpr expressions, in particular, to
omit them the mangled-name without the surrounding X/E. However,
unfortunately, that special case also triggered for ParmVarDecl (a
subtype of VarDecl), and _incorrectly_ emitted 'L_Z .. E' instead of
the proper 'Xfp_E'.
This change causes mangleExpression itself to be responsible for
emitting X/E around non-primary expressions, which removes the
special-case, and corrects both these problems.
Differential Revision: https://reviews.llvm.org/D95487
Now with concepts support merged and mostly complete, we do not need -fconcepts-ts
(which was also misleading as we were not implementing the TS) and can enable
concepts features under C++2a. A warning will be generated if users still attempt
to use -fconcepts-ts.
Implement mangling for CSEs to match regular template-ids.
Reviewed as part of D41569 <https://reviews.llvm.org/D41569>.
Re-commit fixing failing test.
llvm-svn: 375063
